Sunday, 12 April 2015

Sun Coral

Sun Corals are some half a dozen species of coral belonging to the genus Tubastraea. They're found in tropical waters around the world, which is horribly unfair! I'm sure other latitudes would have loved a bit of that sun-shinery but nope, the tropics keep it all for themselves.

Tubastraea comes from the Greek tubus meaning "tube" and astron meaning "star". The astron part is immediately obvious when you see those long tentacles blazing out like sun rays in all their glory.

When the coral retracts its tentacles we can finally take off our sunglasses and get a better view. Now we can see that each tentacle-clad polyp emerges from a tube. These tubes may be up to 4 cm (1.6 in) long or barely there at all. Being a colonial coral, these tubes all emerge from one, common body...

Image: Smithsonian InstitutionTubastraea faulkner

Together they make up one of the more... fleshy galaxies you're likely to see.

Image: Smithsonian InstitutionSkeleton of a star. Or three.

Sun Corals belong to the stony coral group, which means their soft flesh is supported by a tough, calcium carbonate skeleton. A lot of other stony corals look like slabs of rock with tiny tentacles embedded all over the surface. Corals like that are great for building reefs, as you might expect from a good slab of rock.

Sun Corals are different. Their skeletons are comparatively slim and dainty. There's not nearly enough calcium carbonate in there for reef-building.

What they have instead are large polyps topped by long tentacles which hungrily cling to any prey unfortunate enough to swim too close to the suns. Sun Corals have to do that and they have to do it well because they're strict carnivores.

This is unusual for stony corals. Most of those big, bulky corals that live in sun-dappled reefs host symbiotic algae which share some of the products of photosynthesis with their grateful landlords. Sun Corals have no such help, they must feast only on what they can catch with their bare tentacles.

Sounds unfortunate for our hungry Sun Coral, but it does mean they can live in places those other corals can't. Gloomy places. Places which could actually do with a bit of sunshine. So perhaps it's not so unfair for them to be in the sunny tropics.

Sun Corals are mostly found at the mouth of caves or under rocky ledges. They like a good, strong current that will provide them with many opportunities for snatching up food as it passes by.

Oh! And one really cool thing. It's true that most Sun Corals are orange or yellow or peach, but...